title: Free fatty acids inhibit protein tyrosine phosphatase 1B and activate Akt.
abstract: OBJECTIVE
  Accumulating evidence has suggested that free fatty acids (FFAs) interact with protein kinases and protein phosphatases. The present study examined the effect of FFAs on protein phosphatases and Akt.
  
  
  METHODS
  Activities of protein phosphatase 1 (PP1), protein phosphatase 2A (PP2A), and protein tyrosine phosphatase 1B (PTP1B) were assayed under the cell-free conditions. Phosphorylation of Akt was monitored in MSTO-211H human malignant pleural mesothelioma cells without and with knocking-down phosphatidylinositol 3 kinase (PI3K) or 3-phosphoinositide-dependent protein kinase-1 (PDK1).
  
  
  RESULTS
  In the cell-free assay, unsaturated FFAs (uFFAs) such as oleic, linoleic and linolenic acid and saturated FFAs (sFFAs) such as stearic, palmitic, myristic, and behenic acid markedly reduced PTP1B activity, with the potential for uFFAs greater than that for sFFAs. All the investigated sFFAs inhibited PP2A activity, but otherwise no inhibition was obtained with uFFAs. Both uFFAs and sFFAs had no effect on PP1 activity. Oleic acid phosphorylated Akt both on Thr308 and Ser473, while stearic acid phosphorylated Akt on Thr308 alone. The effects of oleic and stearic acid on Akt phosphorylation were abrogated by the PI3K inhibitor wortmannin or the PDK1 inhibitor BX912 and also by knocking-down PI3K or PDK1.
  
  
  CONCLUSIONS
  The results of the present study indicate that uFFAs and sFFAs could activate Akt through a pathway along a PI3K/PDK1/Akt axis in association with PTP1B inhibition.
authors.affiliation: Department of Thoracic Oncology, Hyogo College of Medicine, Nishinomiya, Japan.
authors.forename: Eisuke
authors.initials: E
authors.lastname: Shibata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kanno
authors.forename: Ayako
authors.initials: A
authors.lastname: Tsuchiya
authors.forename: Kohzo
authors.initials: K
authors.lastname: Kuribayashi
authors.forename: Chiharu
authors.initials: C
authors.lastname: Tabata
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakano
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nishizaki
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology*; D006801:Humans; D019308:Palmitic Acid / Q000494:pharmacology; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1 / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D013229:Stearic Acids / Q000494:pharmacology; D017962:alpha-Linolenic Acid / Q000494:pharmacology
chemical_list: D005230:Fatty Acids, Nonesterified; D034741:RNA, Small Interfering; D013229:Stearic Acids; D017962:alpha-Linolenic Acid; D019308:Palmitic Acid; C031183:stearic acid; C516607:PTPN1 protein, human; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1